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Wednesday, February 21, 2007

Over historic time spans there are a number of static variables that determine climate, including: latitude, altitude, proportion of land to water,and proximity to oceans and mountains. Other climate determinants are more dynamic: The thermohaline circulation of the ocean distributes heat energy between the equatorial and polar regions; other ocean currents do the same between land and water on a more regional scale.

Degree of vegetation coverage affects solar heat absorption, water retention, and rainfall on a regional level. Alteration in the quantity of atmospheric greenhouse gases determines the amount of solar energy retained by the planet, leading to global warming or global cooling. The variables which determine climate are numerous and the interactions complex, but there is general agreement that the broad outlines are understood, at least in so far as the determinants of historical climate change are concerned.

Friday, February 16, 2007

Animals are a main group of organisms, classified as the kingdom Animalia or Meta­zoa. In general they are multi­cellular, capable of locomotion, responsive to their environment, and feed by consuming other organisms. Their body plan becomes permanent as they develop, usually early on in their development as embryos, although some undergo a process of metamorphosis later on.

The word "animal" comes from the Latin word animal, of which animalia is the plural, and is derived from anima, meaning vital breath or soul. In everyday usage animal refers to any member of the animal kingdom that is not a human being, and sometimes excludes insects. The use of the word animal in law classically reflects the common pre-scientific use of the word, roughly equivalent to what modern biology would classify as nonhuman mammal. For example, wildlife laws normally use phrases such as "animals, birds and fish."

Monday, February 05, 2007

In music, pitch is the psychological associate of the fundamental frequency of a note. The note an above middle C played on any instrument is perceived to be of the same pitch as a pure tone of 440 Hz, but does not essentially contain a partial having that frequency. Furthermore, a slight change in frequency need not lead to a perceived change in pitch, but a change in pitch implies a change in frequency. In fact, the just perceptible difference is about five cents, but varies over the range of hearing and is more precise when the two pitches are played at the same time. Like other human stimuli, the perception of pitch also can be explained by the Weber-Fechner law.

Pitch also depends on the amplitude of the sound, especially at low frequencies. For instance, a low bass note will sound lower in pitch if it is louder. Like other senses, the comparative perception of pitch can be fooled, resulting in "audio illusions". There are several of these, such as the tritone paradox, but most especially the Shepard scale, where a continuous or discrete sequence of specially formed tones can be made to sound as if the sequence continues ascending or descending forever.